On Fri, 21 Mar 2008 18:33:18 -0700 (PDT), wrote:

I just added a new room to my house. I have installed the windows, and
now I need to know how far the window sill should protrude past the
left and right interior window trim.

Look at a hundred windows by different installers/trimmers and you'll
probably see 30 different styles.

I like a bit of a reveal-- and I also like a thick apron and a deep
sill that will hold a few plants. I've seen sills that wrap around
3 sides of a room- creating a sill/shelf/chair-rail.

Jim